(1) The Comparison of the DNA sequences of the mouse Alpha2(I) collagen and mouse Alpha1(III) collagen promoter regions reveals only a small number of scattered homologies although these two genes are coordinately transcribed in different tissues and coordinately regulated in several transformed cell lines. In contrast, a segment around the translation initiation site is highly conserved in at least three different collagen genes in two different species, suggesting an additional translational control. (2) The cloned Alpha2(I) collagen promoter after it has been stably integrated in the genome of mouse cells responds to the same type of down-regulation by oncogenic proteins as the endogenous Alpha2(I) collagen. (3) Deletions in the mouse Alpha2(I) collagen gene indicate that at least two segments located more that 200 bp and 450 bp upstream of the start of transcription are essential for optimal expression of this gene. (4) The levels of type III and type I collagen mRNA are coordinately regulated by transformation in some but not all mouse fibroblasts.